Transmission control device and method, recording medium, and program

ABSTRACT

This invention relates to a transmission controlling apparatus, a transmission controlling method, a recording medium, and a program for instantaneously transmitting data while averting a so-called slow start. Video data acquired by a picture acquisition unit  21  is input to an initial rate determination unit  24  and a picture encoding unit  22  as outgoing data. An acceptable picture quality determination unit in the initial rate determination unit  24  determines a minimum acceptable picture quality acceptable to a user who views the video data sent from a transmission unit  11.  A transmission rate determination unit in the initial rate determination unit  24  determines as an initial transmission rate the transmission rate that meets criteria for the minimum acceptable picture quality supplied from the acceptable picture quality determination unit, and forwards the determined rate to a rate control unit  25.  In turn, the rate control unit  25  controls the transmission rate for a transmission unit  23  so that the unit  23  starts to send video data at the initial transmission rate supplied from the transmission rate determination unit  44.  This invention applies illustratively to transmitting apparatuses for transmitting predetermined data.

TECHNICAL FIELD

The present invention relates to a transmission controlling apparatus, atransmission controlling method, a recording medium, and a program. Moreparticularly, the invention relates to a transmission controllingapparatus, a transmission controlling method, a recording medium, and aprogram for instantaneously transmitting data over a network whileaverting a so-called slow start.

BACKGROUND ART

Audio and video data (called multimedia data hereunder whereappropriate) is transmitted from sender terminals to receiver terminalsover networks such as the Internet. In such cases, the sender terminalis generally required to adjust the rate at which to transmit multimediadata to the receiver terminal in accordance with network traffic status.Otherwise, the receiver terminal would incur packet losses orpropagation delays, triggering deterioration in the quality of thetransmitted data.

To deal with that problem, the sender terminal controls the rate atwhich to transmit outgoing data. Generally, protocols such as TCP(Transmission Control Protocol) or UDP (User Datagram Protocol) areapplied to the transmission of data over networks. TCP is a transportprotocol that guarantees delivery of data and is highly reliable in datatransmission. In addition, TCP offers arrangements for autonomouslyadjusting transmission rates in keeping with network status. InTCP-based communication, the sender terminal typically begins its datatransmission by sending a single packet to the receiver terminal andwaits for an acknowledgement (ACK) from the latter. Upon receipt of theacknowledgement, the sender terminal sends two packets to the receiverterminal and awaits another acknowledgement. In like manner, the senderterminal increments the number of transmitted packets by one in responseto each acknowledgement received from the receiver terminal.

By the above method, however, the rate at which one terminal sends datato another terminal rises only gradually up to a rate at which thetransmission stabilizes (the rate is called the stable transmission ratehereunder). This phenomenon is what is known as the slow-start problem.

As opposed to TCP, UDP is a protocol which, although often utilized intransmitting audio and video data, has no arrangements for autonomouslyadjusting the rate of data transmission in accordance with networkstatus. To make up for the lacuna, a number of methods have beenproposed by which to adjust the transmission rate under UDP.

A method called TFRC (TCP-Friendly Rate Control) is proposed by R.Rejaje, M. Handley and D. Estrin in “RAP: An end-to-end rate-basedcongestion control mechanism for real-time streams in the Internet,” inProc. of IEEE/INFOCOM '99, March 1999. This method, as with TCP,involves getting the sender side to estimate the state of network loads(traffic status) based on the information returned from the receiverside (called feedback information), whereby the amount of outgoing data(transmission rate) is adjusted autonomously. Because it uses the samescheme as TCP, the TFRC method is also subject to the slow-startproblem.

Another method is proposed by J. Widmer in “Equation-based congestioncontrol,” Diploma Thesis, University of Mannheim, February 2000, <URL:http://www.icir.org/tfrc>. This method, too, involves gradually raisingthe rate of data transmission in response to acknowledgements from thereceiver side. Thus the method also shares the slow-start problem withTCP.

Where multimedia data is transmitted on a streaming basis, theslow-start problem has two ramifications: it takes time to reach thestable transmission rate, and the data transmitted at a low rate can bemeaningless on the receiver side. Illustratively, when streaming videodata is transmitted at a low rate, picture quality can be so poor at thereceiver side that pictures are not acceptable to the user in terms ofquality. In such a case, the user may need to wait for pictures tobecome good enough to watch in quality, i.e., the user may need to waitfor the transmission rate to become sufficiently high so that thequality of the transmitted pictures is acceptable to the user. Withbroadband connections coming into general use today, the contenttransmitted over the network is getting larger in quality so that theuser's expectations for picture quality are higher than ever. The higherthe quality of pictures desired by the user, the longer the user may berequired to wait for satisfactory pictures to arrive because of theslow-start problem.

A technique has been proposed to solve the slow-start problem outlinedabove. The proposed technique involves estimating the bandwidths(transmission rates) of the sender and the receiver sides by use of aprobe packet called a packet pair upon start of a data transmission(e.g., as disclosed in Japanese Patent Laid-open No. 2002-94567, page14, FIGS. 5 and 8).

While it bypasses the slow-start problem, the proposed technique aboveincurs a new problem. That is, from the time the probe packet is sent tothe receiver side until an acknowledgement (ACK) is received for thetransmitted packet (i.e., during the so-called round trip time), thesender side is incapable of starting to send target data such as videodata.

Furthermore, the probe packet has nothing to do with the data desired bythe receiver side. Transmitting such extra data can narrow the bandwidthover the network.

DISCLOSURE OF INVENTION

The present invention has been made in view of the above circumstancesand provides arrangements for instantaneously transmitting data over thenetwork while averting the so-called slow start.

According to one embodiment of the present invention, there is provideda transmission controlling apparatus for controlling transmission ofdata. The apparatus includes: quality determining means for determiningquality of the data in keeping with a property of the data; transmissionrate determining means for determining a transmission rate in accordancewith the quality determined by the quality determining means; andtransmission rate controlling means for controlling the transmissionrate of the data so that the data will start to be transmitted at thetransmission rate determined by the transmission rate determining means.

Preferably, the data may constitute pictures, and the property of thedata may be a picture property.

The picture property may preferably be at least one of an applicationproperty, a content property, and an imaging device property.

Preferably, the inventive transmission controlling apparatus may furtherinclude storing means for storing the data of which the quality isassociated with the picture property. The quality determining means maydetermine the quality based on the data stored in the storing means.

Preferably, the data may constitute pictures encoded by a predeterminedencoding method, and the transmission rate determining means maydetermine the transmission rate based on a picture size of the picturesand on a relationship between the quality associated with the encodingmethod on the one hand and the transmission rate on the other hand.

Preferably, the inventive transmission controlling apparatus may furtherinclude information inputting means for inputting information about theproperty of the data from outside the transmission controllingapparatus. The quality determining means may determine the quality inaccordance with the information input by the information inputtingmeans.

The transmission rate controlling means may preferably control thetransmission rate of the data so that after the transmission of the datahas started, the rate of the transmission will not be lowered below thetransmission rate supplied from the transmission rate determining means.

The transmission rate controlling means may preferably control thetransmission rate of the data so that in case of a communicationtime-out of the data, the transmission of the data will be resumed atthe transmission rate determined by the transmission rate determiningmeans.

According to another embodiment of the present invention, there isprovided a transmission controlling method for controlling transmissionof data. The method includes the steps of: determining quality of thedata in keeping with a property of the data; determining a transmissionrate in accordance with the quality determined in the qualitydetermining step; and controlling the transmission rate of the data sothat the data will start to be transmitted at the transmission ratedetermined in the transmission rate determining step.

According to a further embodiment of the present invention, there isprovided a recording medium which stores in computer-readable fashion aprogram for controlling transmission of data. The program includes thesteps of: determining quality of the data in keeping with a property ofthe data; determining a transmission rate in accordance with the qualitydetermined in the quality determining step; and controlling thetransmission rate of the data so that the data will start to betransmitted at the transmission rate determined in the transmission ratedetermining step.

According to an even further embodiment of the present invention, thereis provided a program for controlling transmission of data and forcausing a computer to execute a procedure including the steps of:determining quality of the data in keeping with a property of the data;determining a transmission rate in accordance with the qualitydetermined in the quality determining step; and controlling thetransmission rate of the data so that the data will start to betransmitted at the transmission rate determined in the transmission ratedetermining step.

Where the transmission controlling apparatus, transmission controllingmethod, recording medium, and program according to this invention are inuse, the quality of data to be transmitted is determined in keeping withthe property of the data in question. The rate at which to transmit thedata is established in accordance with the data quality thus determined.Data transmission is controlled in such a manner that the data startsgetting transmitted at the established transmission rate.

The transmission controlling apparatus may be either an independentapparatus or a block for handling transmission control processing in anapparatus.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing a typical configuration of acommunication system to which this invention is applied;

FIG. 2 is a block diagram showing a typical structure of a transmittingapparatus practiced as a first embodiment of the invention and includedin the diagram of FIG. 1;

FIG. 3 is a block diagram showing a typical structure of an initial ratedetermination unit included in the diagram of FIG. 2;

FIG. 4A is a tabular view that lists data stored in a database includedin the diagram of FIG. 3;

FIG. 4B is a graphic representation showing data stored in the databaseshown in FIG. 3;

FIG. 5A is a graphic representation showing relations betweentransmission rates used by the transmission rate determination unit inFIG. 3 on the one hand, and picture qualities on the other hand;

FIG. 5B is another graphic representation showing relations betweentransmission rates used by the transmission rate determination unit inFIG. 3 on the one hand, and picture qualities on the other hand;

FIG. 6 is a flowchart of steps constituting a transmission ratedetermining process performed by the transmitting apparatus in FIG. 1;

FIG. 7 is a flowchart of steps constituting an acceptable picturequality determining process in step S2 of FIG. 6;

FIG. 8 is a flowchart of steps constituting an initial transmission ratedetermining process in step S3 of FIG. 6;

FIG. 9 is a graphic representation showing relations between the elapsedtime since the start of transmission by the transmitting apparatus ofFIG. 1 on the one hand and transmission rates on the other hand, as wellas relations between the elapsed time since the start of transmission bya conventional setup on the one hand and transmission rates on the otherhand;

FIG. 10 is a block diagram showing a typical structure of a transmittingapparatus practiced as a second embodiment of the invention and includedin the diagram of FIG. 1;

FIG. 11 is a block diagram showing a typical structure of an initialrate determination unit included in the diagram of FIG. 10; and

FIG. 12 is a block diagram showing a typical structure of a computer towhich this invention is applied.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 shows a typical configuration of a communication system to whichthis invention is applied. In FIG. 1, a transmitting apparatus 11 isconnected to a receiving apparatus 13 via a network 12 such as theInternet. A picture acquisition unit 21 (FIG. 2) in the transmittingapparatus 11 acquires pictures. The apparatus 11 encodes the acquiredpictures using a suitable encoding method such as MPEG-4 (Moving PictureExperts Group Phase 4) or JPEG (Joint Photographic Experts Group) 2000,thus generating packets constituting the encoded video data. Thetransmitting apparatus 11 transmits the generated packets to thereceiving apparatus 13 over the network 12. From the receiving apparatus13, the transmitting apparatus 11 receives feedback information such asacknowledgements (ACK) for the packets having been sent.

The receiving apparatus 13 receives the packets from the transmittingapparatus 11, acquires video data from the received packets, and has thedata displayed on a display unit (not shown) such as a CRT (Cathode RayTube) unit or an LCD (Liquid Crystal Display). In response to thepackets received from the transmitting apparatus 11, the receivingapparatus 13 generates feedback information such as acknowledgements(ACK) and returns the feedback information to the transmitting apparatus11.

For purpose of simplification and illustration, the transmittingapparatus 11 is shown independent of the receiving apparatus 13 in thisdescription. In practice, however, the transmitting apparatus 11 may bedesigned also to function as the receiving apparatus 13 and thereceiving apparatus 13 may also be given the capabilities of thetransmitting apparatus 11.

FIG. 2 shows a typical structure of the transmitting apparatus 11practiced as the first embodiment of the invention. An operation unit 27accepts the user's operation input and notifies relevant blocks in theapparatus of the operation information corresponding to the user'soperation thus accepted. Illustratively, by manipulating the operationunit 27, the user designates a video data compression method (i.e.,encoding method) such as MPEG-4 or JPEG 2000 for use in sending videodata to the receiving apparatus 13 (FIG. 1). Information designating thecompression method (encoding method) is supplied from the operation unit27 to a picture encoding unit 22 and an initial rate determination unit24. The operation unit 27 also supplies the initial rate determinationunit 24 with a property of the application set by the user manipulatingthe operation unit 27. The properties of the application will bediscussed later.

The picture acquisition unit 21 is formed illustratively by a camcorderor a digital video camera. The picture acquisition unit 21 takespictures of a subject and supplies the picture encoding unit 22 andinitial rate determination unit 24 of the video data constituting theimaged object. The video data is typically composed of a brightnesssignal (Y), of the difference between the brightness signal and a redcomponent (U), and of the difference between the brightness signal and ablue component (V) in the YUV format.

As described, when the user designates the encoding method bymanipulating the operation unit 27, the information denoting thedesignated encoding method is supplied from the operation unit 27 to thepicture encoding unit 22. The picture encoding unit 22 encodes the videodata coming from the picture acquisition unit 21 through the use of theencoding method such as MPEG-4 or JPEG 2000 designated and supplied fromthe operation unit 27. The video data thus encoded (called the encodeddata hereunder) is forwarded from the picture encoding unit 22 to atransmission unit 23.

Given the encoded data from the picture encoding unit 22, thetransmission unit 23 splits the received data to packetize into aplurality of packets called data packets. The transmission unit 23prefixes each of the generated data packets with a packet head of TCP/IP(Transmission Control Protocol/Internet Protocol) or UDP/IP (UserDatagram Protocol/Internet Protocol). In keeping with a timing commandcoming from a rate control unit 25, to be described later, thetransmission unit 23 transmits the data packets each furnished with thepacket header. (the packet header-prefixed packets will simply calledthe packets hereunder) to the receiving apparatus 13 through a networkinterface unit 26.

The initial rate determination unit 24 is supplied with picture-relatedproperties both from the picture acquisition unit 21 and from outsidethe transmitting apparatus 11. The initial rate determination unit 24 isalso fed by the operation unit 27 with the information denoting theencoding method selected by the user manipulating the operation unit 27.Based on the property of the pictures in question and on the designatedencoding method, the initial rate determination unit 24 determines aminimum picture quality acceptable to the user who views the picturesreceived by the receiving apparatus 13. Furthermore, the initial ratedetermination unit 24 determines a transmission rate that satisfies theminimum picture quality and supplies the determined transmission rate tothe rate control unit 25 as an initial transmission rate. Structuraldetails of the initial rate determination unit 24 and specific pictureproperties will be discussed later in reference to FIG. 3. In theensuing description, the lowest quality of pictures acceptable to theuser viewing the pictures will be called the minimum acceptable picturequality.

The rate control unit 25 controls the transmission rate at which thetransmission unit 23 transmits packets. More specifically, when thetransmission unit 23 transmits a first packet, the rate control unit 25supplies the transmission unit 23 with a timing command for causing thefirst packet to be transmitted at the initial transmission rate fed fromthe initial rate determination unit 24. For transmission of the secondand subsequent packets, the rate control unit 25 determines atransmission rate based on the feedback information coming from thereceiving apparatus 13 through the network interface unit 26. The ratecontrol unit 25 then supplies the transmission unit 23 with a timingcommand such that the packets will be transmitted at the determinedtransmission rate.

When the display unit displays the video data transmitted from thetransmitting apparatus 11 to the receiving apparatus 13 at the initialtransmission rate, the quality of the displayed pictures (i.e., picturequality) is the lowest quality appropriated for streaming data. That isbecause the initial transmission rate is determined as representative ofthe lowest picture quality acceptable to the user viewing the receivedpictures. If the pictures were transmitted at a rate lower than theinitial transmission rate, the quality of the pictures would be lessthan that is acceptable to the user. That means the rate control unit 25cannot let the transmission rate at which the transmission unit 23 sendspackets become lower than the initial transmission rate. In other words,the initial transmission rate is both the rate at which the transmissionunit 23 starts data transmission and the lowest limit of transmissionrates for communication. The rate control unit 25 thus determinesadaptively the transmission rate in keeping with the feedbackinformation coming from the receiving apparatus 13 through the networkinterface unit 26, making sure that the determined rate does not becomelower than the initial transmission rate supplied from the initial ratedetermination unit 24.

It might happen that the feedback information corresponding to thepackets sent by the transmission unit 23 is not received by the networkinterface unit 26, i.e., that a communication time-out is detectedbetween the transmitting apparatus 11 and the receiving apparatus 13, sothat the rate control unit 25 cannot determine the rate at which totransmit the next packet based on the feedback information. In such acase, the rate control unit 25 resets the transmission rate at which thetransmission unit 23 sends the next packet, to the initial transmissionrate supplied from the initial rate determination unit 24. Thetransmission unit 23 is then controlled to transmit the next packet atthe initial transmission rate thus supplied.

The network interface unit 26 outputs the packets coming from thetransmission unit 23 to the receiving apparatus 13 over the network 12.The network interface unit 26 also gives the rate control unit 25 thefeedback information sent from the receiving apparatus 13 over thenetwork 12.

FIG. 3 is a block diagram showing a typical internal structure of theinitial rate determination unit 24 included in FIG. 2.

Based on the property of the pictures being acquired by the pictureacquisition unit 21 (FIG. 2), the initial rate determination unit 24first determines the lowest picture quality acceptable to the user(i.e., minimum acceptable picture quality) viewing the pictures receivedby the receiving apparatus 13 (FIG. 1). The initial rate determinationunit 24 then decides on a transmission rate that satisfies the picturequality thus determined and supplies the rate control unit 25 (FIG. 2)with that rate as the initial transmission rate.

The picture property may be any one of an application property, acontent property, and an imaging device property.

The application property is one of, say, four categories of contentrepresented by teleconference, news program, baseball telecast, andsoccer telecast. Typically, the news program is a program that shows aperson or persons in the middle of the screen against a background thatmoves sporadically. The teleconference is a program that shows a personor persons in the middle of the screen against a background that remainsmostly static. Because of a high demand for depicting the facialexpressions of the people being imaged, the picture quality required ofthe teleconference is higher than that of the news program. Comparedwith the baseball telecast, the soccer telecast is required to emphasizetwo teams being constantly in motion on a single playing field. Thatmeans the picture quality required of the soccer telecast emphasizingmovements is lower than that of the baseball telecast. The userdesignates the application property (e.g., teleconference, news program,baseball telecast, or soccer telecast) by manipulating the operationunit 27. The information thus designated is supplied from the operationunit 27 to an acceptable picture quality determination unit 42.

The property of content represents a degree of the visual noise incontent as perceived by the humans. Illustratively, pictures of rapidmovements or pictures full of small details are not perceived by thehumans to be as much degraded in quality as the high compression rate inuse would suggest. Defining the property of content thus involves takinginto consideration the characteristics of the humans' sense of sight.The property of a given content may be represented illustratively by thedegree of rapidity of motions in the pictures of that content. Therapidity of motions in pictures is typically obtained by firstextracting frame-by-frame pictures at predetermined intervals from thevideo data fed from the picture acquisition unit 21 to the initial ratedetermination unit 24, and by acquiring chronologically the differencesbetween the frame pictures in terms of correspondingly moving pixelsfound therebetween.

The property of an imaging device signifies how much the device affectsthe perceived noise in content. Illustratively, pictures taken by arapidly moving digital video camera are not perceived by the humans tobe as corrupted in quality as the elevated compression rate in use wouldimply. If the picture acquisition unit 21 is a digital video camera,information indicating whether the camera was moving or fixed whiletaking pictures may be adopted as the imaging device property. Thatinformation may illustratively be represented by the traveling speed ofthe digital video camera. When acquired outside the transmittingapparatus 11, the value of the camera speed may be supplied to anexternal interface unit 41. If the digital video camera was fixed andstationary, information indicating that the traveling speed of thecamera is zero is sent to the external interface unit 41. Whereas theproperty of the imaging device is similar to the property of content, itis easier to obtain the traveling speed of the device as an objectivelymeasured value than a value representative of the content property.

The external interface unit 41 receives the above-described imagingdevice property (i.e., traveling speed) from outside the transmittingapparatus 11, and forwards the received property to the acceptablepicture quality determination unit 42.

Based on the video data fed from the picture acquisition unit 21, theacceptable picture quality determination unit 42 calculates theabove-mentioned picture motions (i.e., content property). In referenceto a database 43, the acceptable picture quality determination unit 42determines a minimum acceptable picture quality based on the applicationproperty sent from the operation unit 27, on the picture motions (i.e.,content property) calculated from the video data coming from the pictureacquisition unit 21, and on the traveling speed (i.e., imaging deviceproperty) supplied from the external interface unit 41. The minimumacceptable picture quality thus determined is forwarded from theacceptable picture quality determination unit 42 to a transmission ratedetermination unit 44. For this embodiment of the invention, it isassumed that the application property is selected from four options,i.e., teleconference, news program, baseball telecast, and soccertelecast; that the content property is furnished by the picture motions;and that the imaging device property is provided by the traveling speedof the picture acquisition unit 21.

The database 43 is arranged to retain in advance a table associatingapplication properties with minimum allowable picture qualities, as wellas data denoting relations between picture motions and the minimumallowable picture qualities, as shown in FIGS. 4A and 4B. The table andthe data in the database 43 have been obtained by carrying outexperiments with an indefinite number of users and by statisticallyprocessing what the experiments showed, i.e., the picture qualitiesgenerally acceptable to the user for different categories of content.Illustratively, baseball telecasts with varying picture qualities wereshown to the users participating in the experiments. In response, theusers decided on the picture qualities deemed acceptable for theirviewing. The resulting data was tallied up to establish the picturequality generally deemed acceptable to the user viewing the baseballtelecast. The picture quality may be represented illustratively by theS/N ratio (Signal to Noise Ratio) of pictures.

FIG. 4A shows a table that associates application properties withminimum acceptable picture qualities. When the application propertydenotes teleconferences, the corresponding minimum acceptable picturequality is set to D₁. For the application property denoting newsprograms, the corresponding minimum acceptable picture quality is set toD₂. Likewise, the minimum acceptable picture quality is set to D₃ forthe application property denoting baseball telecasts and to D₄ for theapplication property denoting soccer telecasts. Although this embodimentof the invention adopts four application properties corresponding to thecategories of teleconferences, news programs, baseball telecasts, andsoccer telecasts, this is not limitative of the invention.Alternatively, other categories may be added as needed such as concerttelecasts.

FIG. 4B graphically shows relations between picture motions as thecontent property on the one hand, and minimum acceptable picturequalities on the other hand. The relationship between the picture motionm and the minimum acceptable picture quality D is defined by theexpression D=f_(x)(m) based on the function f_(x)( ) as shown in FIG. 4Band is held in the database 43. For example, suppose that the acceptablepicture quality determination unit 42 has calculated ml as the picturemotion based on the video data supplied from the picture acquisitionunit 21. In that case, the acceptable picture quality determination unit42 obtains the minimum acceptable picture quality D_(m1) correspondingto the picture motion ml through the use of the function D=f_(x)(m)indicated in FIG. 4B.

Although the figures above show no example of data associating travelingspeeds as the property of the imaging device with minimum acceptablepicture qualities, such relations can also be expressed in a mannersimilar to what is shown in FIG. 4B. The only difference betweentraveling speeds and picture motions is whether the moving object is thepicture acquisition unit 21 (i.e., traveling speed) or the subject beingimaged (picture motion). For that reason, the relationship between thetraveling speed m and the minimum acceptable picture quality D is alsodefined by the expression D=f_(x)(m) in FIG. 4B, and the traveling speedwill not be discussed further.

Alternatively, the relationship between picture motions and minimumacceptable picture qualities may be defined not by the function f_(x)( )(i.e., D=f_(x)(m) in FIG. 4B) but by a scheme whereby picture motionsare split into predetermined ranges associated with varying minimumacceptable picture qualities. Under this scheme, the relations betweenthe picture motions and the minimum acceptable picture qualities may beexpressed in a table such as the one in FIG. 4A.

As described, in reference to the database 43, the acceptable picturequality determination unit 42 determines a minimum acceptable picturequality D_(i) (i=one of 1 through 4) based on the application propertyand another minimum acceptable picture quality D_(m1) based on thecontent property. With the minimum acceptable picture qualities D_(i)and D_(m1) thus determined, the acceptable picture quality determinationunit 42 decides on a definitive minimum acceptable picture quality D andsupplies it to the transmission rate determination unit 44.Illustratively, the definitive minimum acceptable picture quality D maybe determined by selecting whichever is the higher of the minimumacceptable picture quality D_(i) (i=one of 1 through 4) derived from theapplication property and the minimum acceptable picture quality D_(m1)derived from the picture motion (traveling speed) based on the contentproperty (picture quality).

The database 43 should preferably be updated periodically. That isbecause subsequent experiments and experiences are expected to promptchanges in the table that associates application properties with minimumacceptable picture qualities, as well as in the relations betweencontent properties and the minimum acceptable picture qualities.Illustratively, the database 43 may be stored on a removable storagemedium. This allows the storage medium, along with the database 43 heldthereon, to be replaced when any of the data in the database 43 has beenupdated. As another alternative, the database 43 may be connected to thenetwork 12 and updated by acquiring updated data from servers or likesources on the network 12.

Returning to FIG. 3, the transmission rate determination unit 44 in theinitial rate determination unit 24 is supplied with information denotingthe compression method (i.e., encoding method) for use in compressingvideo data. The method-designating information is set by the usermanipulating the operation unit 27 and is sent from the operation unit27. As in the case of the acceptable picture quality determination unit42, the transmission rate determination unit 44 is fed with the videodata acquired by the picture acquisition unit 21. From the video datasupplied by the picture acquisition unit 21, the transmission ratedetermination unit 44 obtains a picture size such as the SD (StandardDefinition) size or SIF (Source Input Format) size. Based on theacquired picture size and on the encoding method sent from the operationunit 27, the transmission rate determination unit 44 decides on thetransmission rate corresponding to the quality (minimum acceptablepicture quality) supplied from the acceptable picture qualitydetermination unit 42. The transmission rate thus determined is suppliedfrom the transmission rate determination unit 44 to the rate controlunit 25 (FIG. 2) as the initial transmission rate. It should be notedthat the SD size represents 720 by 480 pixels per picture taken and theSIF size denotes 360 by 240 pixels per picture.

What follows is a discussion of relations between the picture size andpicture compression rate on the one hand, and bandwidths (i.e.,transmission rates) on the other hand. With all other conditions madeequal, the SD size picture obviously requires a greater bandwidth (i.e.,higher transmission rate) than the SIF size picture when they aretransmitted. When video data is sent from the transmitting apparatus 11to the receiving apparatus 13, the data is compressed by the pictureencoding unit 22 as mentioned above before being output onto the network12. It follows that raising the compression rate at which the pictureencoding unit 22 compresses (i.e., encodes) the video data reduces thebandwidth (transmission rate) necessary for transmitting the data overthe network 12. However, higher compression rates used by the pictureencoding unit 22 for its compressing (encoding) process translate intopoorer picture qualities. In other words, the relations between picturequalities and transmission rates are specific to each picture size andencoding method (compression rate), as depicted in FIGS. 5A and 5B.

FIG. 5A shows relations between the picture quality D for SD and SIFsize pictures on the one hand, and the transmission rate B on the otherhand, with MPEG-4 adopted as the encoding method. FIG. 5B indicatesrelations between the picture quality D for SD and SIF size pictures onthe one hand, and the transmission rate B on the other hand, with JPEG200 selected as the encoding method.

In FIG. 5A, the relationship between the picture quality and thetransmission rate is defined by the function B=f_(a)(D) where thepicture size acquired by the transmission rate determination unit 44based on the video data coming from the picture acquisition unit 21 isthe SD size, i.e., where the picture acquisition unit 21 outputs SD sizepictures. The relationship between the picture quality and thetransmission rate is defined by the function B=f_(b)(D) where thepicture size obtained by the transmission rate determination unit 44based on the video data from the picture acquisition unit 21 is the SIFsize, i.e., where the picture acquisition unit 21 outputs SIF sizepictures. It follows that when the picture quality (minimum acceptablepicture quality) supplied from the minimum acceptable picture qualitydetermination unit 42 to the transmission rate determination unit 44 isD_(1A), the transmission rate is defined by the functionB₁=f_(a)(D_(1A)) if the pictures have the SD size, or byB₀=f_(b)(D_(1A)) if the pictures have the SIF size.

In FIG. 5B, the relationship between the picture quality and thetransmission rate is defined by the function B=f_(c)(D) where thepicture size acquired by the transmission rate determination unit 44based on the video data coming from the picture acquisition unit 21 isthe SD size, i.e., where the picture acquisition unit 21 outputs SD sizepictures. The relationship between the picture quality and thetransmission rate is defined by the function B=f_(d)(D) where thepicture size obtained by the transmission rate determination unit 44based on the video data from the picture acquisition unit 21 is the SIFsize, i.e., where the picture acquisition unit 21 outputs SIF sizepictures. It follows that when the picture quality (minimum acceptablepicture quality) supplied from the minimum acceptable picture qualitydetermination unit 42 to the transmission rate determination unit 44 isD_(1B), the transmission rate is defined by the functionB₃=f_(c)(D_(1B)) if the pictures have the SD size, or byB₂=f_(d)(D_(1B)) if the pictures have the SIF size.

The data representative of the relations between picture qualities andtransmission rates as indicated in FIGS. 5A and 5B is held inside thetransmission rate determination unit 44. Based on these relations withregard to the size and encoding method of the pictures acquired by thepicture acquisition unit 21, the transmission rate determination unit 44determines the transmission rate corresponding to the minimum acceptablepicture quality supplied from the acceptable picture qualitydetermination unit 42. The transmission rate thus determined is sentfrom the transmission rate determination unit 44 to the rate controlunit 25 as the initial transmission rate.

For this embodiment of the invention, two picture sizes are assumed,i.e., SD size and SIF size, with respect to the pictures taken by thepicture acquisition unit 21. However, this is not limitative of theinvention. Alternatively, other sizes may be adopted, such as the HD(High Definition) size (denoting 1920 by 1080 pixels).

The video data encoding method (compression method) designated by theuser manipulating the operation unit 27 is not limited to MPEG-4 or JPEG2000. Other encoding methods may also be adopted, such as MPEG-2.

If any of these alternative picture sizes and encoding methods is to beadopted, the relations between picture qualities and transmission ratesregarding the new picture size and/or encoding method will be set anewin the transmission rate determination unit 44 as plotted in FIGS. 5Aand 5B. For any picture size, any encoding method (compression method),or any compression rate that may be adopted, the higher the picturequality, the higher the transmission rate required (i.e., the broaderthe bandwidth).

Although the relations between the minimum acceptable picture qualityand the transmission rate with respect to the picture size and encodingmethod of interest as depicted in FIGS. 5A and 5B are assumed to beestablished inside the transmission rate determination unit 44, this isnot limitative of the invention. Alternatively, these relations may beplaced in the database 43 from which they may be retrieved as needed,just like the relations between minimum acceptable picture qualities andapplication properties as well as the relations between minimumacceptable picture qualities and picture motions indicated in FIGS. 4Aand 4B.

Referring to the flowchart of FIG. 6, the transmission rate determiningprocess performed by the transmitting apparatus 11 will now bedescribed. This process is initiated either by the user manipulating theoperation unit 27, or by the transmitting apparatus 11 starting to sendvideo data in response to a request from the receiving apparatus 13.

In step S1, the initial rate determination unit 24 sets the initialtransmission rate to zero and supplies it to the rate control unit 25 asthe initial value. Control is passed from step S1 to step S2.

In step S2, the acceptable picture quality determination unit 42 in theinitial rate determination unit 24 carries out an acceptable picturequality determining process. Step S2 is followed by step S3. Theacceptable picture quality determining process, to be discussed later indetail with reference to FIG. 7, allows the acceptable picture qualitydetermination unit 42 to determine a minimum acceptable picture qualitybased on the application property and picture motion in effect. Theminimum acceptable picture quality thus determined is supplied to thetransmission rate determination unit 44.

In step S3, the transmission rate determination unit 44 carries out aninitial transmission rate determining process based on the minimumacceptable picture quality supplied from the acceptable picture qualitydetermination unit 42 in step S2. Control is passed from step S3 to stepS4. It is assumed that the initial transmission rate determined in theinitial transmission rate determining process is represented byreference character B. The initial transmission rate determining processwill be discussed later in detail with reference to FIG. 8.

In step S4, the transmission rate determination unit 44 supplies therate control unit 25 with the initial transmission rate B determined bythe unit 44 in step S3. Step S4 is followed by step S5.

In step S5, the rate control unit 25 carries out rate control byresorting to the TFRC method. More specifically, the rate control unit25 gives the transmission unit 23 a timing command causing the unit 23to establish the initial transmission rate B that was sent from thetransmission rate determination unit 44 in step S4. Control is passedfrom step S5 to step S6.

In step S6, the rate control unit 25 checks to determine whethertransmission of the video data acquired by the picture acquisition unit21 has ended, i.e., whether the packets sent from the transmission unit23 to the receiving apparatus 13 through the network interface unit 26have been exhausted. If the transmission of the video data is not foundto have ended in step S6, step S7 is reached. In step S7, the ratecontrol unit 25 checks to determine whether a time-out has occurred,i.e., whether feedback information is supplied from the networkinterface unit 26 in response to the packets sent by the transmissionunit 23.

If no time-out is detected in step S7, the rate control unit 25 returnsto step S5 and repeats steps S5 through S7. During the process, the ratecontrol unit 25 determines adaptively the transmission rate based on thefeedback information coming from the network interface unit 26. Fortransmission rate control, the rate control unit 25 gives thetransmission unit 23 a timing command causing the unit 23 to establishedthe transmission rate thus determined.

If a time-out is detected in step S7, i.e., if the rate control unit 25is not supplied with feedback information from the network interfaceunit 26 in response to the packets sent by the transmission unit 23,then the rate control unit 25 returns to step S4 and repeats thesubsequent steps. That is, the rate control unit 25 resets thetransmission rate to the initial transmission rate B for transmissionrate control.

When the transmission of the video data is found to have ended in stepS6, the transmission rate determining process is terminated.

The acceptable picture quality determining process performed by theacceptable picture quality determination unit 42 in step S2 of FIG. 6 isdescribed below with reference to the flowchart of FIG. 7.

In step S21, the acceptable picture quality determination unit 42acquires the application property supplied from the operation unit 27.Control is passed from step S21 to step S22.

In step S22, the acceptable picture quality determination unit 42 checksto determine whether the application property acquired in step S21 isrepresentative of the teleconference. If in step S22 the applicationproperty is found to represent the teleconference, the acceptablepicture quality determination unit 42 goes to step S23. In step S23, theacceptable picture quality determination unit 42 adopts (i.e.,determines) D₁ as the minimum acceptable picture quality by referencingthe table which resides in the database 43 and is shown in FIG. 4A. Fromstep S23, control is passed on to step S30.

If in step S22 the application property is not found to berepresentative of the teleconference, step S24 is reached. In step S24,the acceptable picture quality determination unit 42 checks to determinewhether the application property acquired in step S21 is representativeof the news program. If in step S24 the application property is found torepresent the news program, the acceptable picture quality determinationunit 42 goes to step S25. In step S25, the acceptable picture qualitydetermination unit 42 adopts D₂ as the minimum acceptable picturequality by referencing the table which resides in the database 43 and isshown in FIG. 4A. From step S25, control is passed on to step S30.

If in step S24 the application property is not found to berepresentative of the news program, step S26 is reached. In step S26,the acceptable picture quality determination unit 42 checks to determinewhether the application property acquired in step S21 is representativeof the baseball telecast. If in step S26 the application property isfound to represent the baseball telecast, the acceptable picture qualitydetermination unit 42 goes to step S27. In step S27, the acceptablepicture quality determination unit 42 adopts D₃ as the minimumacceptable picture quality by referencing the table which resides in thedatabase 43 and is shown in FIG. 4A. From step S27, control is passed onto step S30.

If in step S26 the application property is not found to berepresentative of the baseball telecast, step S28 is reached. In stepS28, the acceptable picture quality determination unit 42 checks todetermine whether the application property acquired in step S21 isrepresentative of the soccer telecast. If in step S28 the applicationproperty is found to represent the soccer telecast, the acceptablepicture quality determination unit 42 goes to step S29. In step S29, theacceptable picture quality determination unit 42 adopts D₄ as theminimum acceptable picture quality by referencing the table whichresides in the database 43 and is shown in FIG. 4A. From step S29,control is passed on to step S30.

If in step S28 the application property is not found to berepresentative of the soccer telecast, step S30 is also reached. In stepS30, the acceptable picture quality determination unit 42 calculates thepicture motion ml from the video data supplied by the pictureacquisition unit 21. By referencing the relations between the picturemotion m and the minimum acceptable picture quality D held in thedatabase 43 and shown in FIG. 4B, the acceptable picture qualitydetermination unit 42 adopts D_(m1) as the minimum acceptable picturequality corresponding to the calculated picture motion ml. Step S30 isfollowed by step S31.

In step S31, the acceptable picture quality determination unit 42determines a definitive minimum acceptable picture quality D based onboth the minimum acceptable picture quality D_(i) (i=one of 1 through 4)calculated from the application property and on the minimum acceptablepicture quality D_(m1) derived from the picture motion m1. The minimumacceptable picture quality D thus determined is supplied to thetransmission rate determination unit 44, and control is returned to theprocess of FIG. 6. If D₁ is less than D_(m1) and if the applicationproperty supplied from the operation unit 27 to the acceptable picturequality determination unit 42 is representative of the teleconference,then the picture quality D_(m1) is determined as the ultimate minimumacceptable picture quality D. That is because the picture quality D_(m1)is the higher of the minimum acceptable picture quality D₁ adopted instep S23 and the minimum acceptable picture quality D_(m1) adopted instep S30.

Referring to the flowchart of FIG. 8, the initial transmission ratedetermining process performed by the transmission rate determinationunit 44 in step S3 of FIG. 6 will now be described.

In step S51, the transmission rate determination unit 44 acquires theuser-designated video data encoding method supplied from the operationunit 27. From step S51, control is passed on to step S52.

In step S52, the transmission rate determination unit 44 checks todetermine whether the encoding method acquired in step S51 is MPEG-4,i.e., whether the pictures sent by the transmitting apparatus 11 to thereceiving apparatus 13 are encoded using the MPEG-4 standard. If in stepS52 the pictures sent by the transmitting apparatus 11 to the receivingapparatus 13 are not found to be encoded using the MPEG-4 standard, stepS53 is reached. In step S53, the transmission rate determination unit 44checks to determine whether the pictures sent by the transmittingapparatus 11 to the receiving apparatus 13 are encoded using the JPEG2000 standard.

If in step S53 the pictures sent by the transmitting apparatus 11 to thereceiving apparatus 13 are not found to be encoded using the JPEG 2000standard, then the transmission rate determination unit 44 determines aninitial transmission rate B_(D) as the default, supplies it to the ratecontrol unit 25, and terminates the process. The situation in whichneither MPEG-4 nor JPEG 2000 applies occurs illustratively when the userfails to designate any encoding method. In such a case, the transmissionrate determination unit 44 may select as the initial transmission rateB_(D) the lowest transmission rate relative to the minimum acceptablepicture quality D supplied from the acceptable picture qualitydetermination unit 42. The selection is made with respect to therelational expressions (in FIGS. 5A and 5B) prepared beforehand in thetransmission rate determination unit 44, the expressions defining therelations between picture qualities and transmission rates.

If in step S53 the pictures sent by the transmitting apparatus 11 to thereceiving apparatus 13 are found to be encoded using the JPEG 2000standard, step S55 is reached. In step S55, the transmission ratedetermination unit 44 checks to determine whether the pictures acquiredby the picture acquisition unit 21 have the SD size.

If in step S55 the pictures acquired by the picture acquisition unit 21are found to have the SD size, step S56 is reached. In step S56, thetransmission rate determination unit 44 selects the function B=f_(c)(D)shown in FIG. 5B, and goes to step S61.

If in step S55 the pictures acquired by the picture acquisition unit 21are not found to have the SD size, i.e., if the pictures are found tohave the SIF size, then step S57 is reached. In step S57, thetransmission rate determination unit 44 selects the function B=f_(d)(D)shown in FIG. 5B, and goes to step S61.

If in step S52 the pictures sent by the transmitting apparatus 11 to thereceiving apparatus 13 are found to be encoded using the MPEG-4standard, step S58 is reached. In step S58, the transmission ratedetermination unit 44 checks to determine whether the pictures acquiredby the picture acquisition unit 21 have the SD size.

If in step S58 the pictures acquired by the picture acquisition unit 21are found to have the SD size, step S59 is reached. In step S59, thetransmission rate determination unit 44 selects the function B=f_(a)(D)shown in FIG. 5A, and goes to step S61.

If in step S58 the pictures acquired by the picture acquisition unit 21are not found to have the SD size, i.e., if the pictures are found tohave the SIF size, then step S60 is reached. In step S60, thetransmission rate determination unit 44 selects the function B=f_(b)(D)shown in FIG. 5A, and goes to step S61.

In step S61, using the function selected in step S56, S57, S59, or S60,the transmission rate determination unit 44 calculates the transmissionrate B corresponding to the minimum acceptable picture quality Dsupplied from the acceptable picture quality determination unit 42.Thereafter, control is returned to the process of FIG. 6.

FIG. 9 is a graphic representation showing relations between the elapsedtime since the start of video data transmission by the transmittingapparatus 11 of FIG. 1 on the one hand and transmission rates on theother hand, as well as relations between the elapsed time since thestart of video data transmission by a conventional setup on the one handand transmission rates on the other hand. The conventional setupinvolves starting the transmitting process with a single packet andincrementing the number of transmitted packets by one every time anacknowledgement (ACK) has been returned from the receiver side.

A line L1 represents the relations between the elapsed time since thestart of data transmission by the transmitting apparatus 11 of FIG. 1 onthe one hand and transmission rates on the other hand. The transmittingapparatus 11 starts communication (i.e., video data transmission) at aninitial transmission rate B₁. On receiving an acknowledgement uponelapse of a time period RTT, the transmitting apparatus 11 raises thetransmission rate by a predetermined level and proceeds to carry out thenext transmission. This transmission rate control is repeated by thetransmitting apparatus 11 given the feedback information correspondingto the transmitted packets. As a result, a stable transmission rateB_(stable) is reached a time period T1 after the start of datatransmission. If the transmitting apparatus 11 starts communication(i.e., video data transmission) at the initial transmission rate B₁ andfails to receive the feedback information corresponding to thetransmitted packets due to traffic status on the network 12, i.e., if acommunication time-out has occurred during the first data transmission,the transmitting-apparatus 11 may repeat the first transmission byestablishing half the initial transmission rate B₁ (i.e., (B₁)/2) as theinitial transmission rate.

Another line L0 denotes the relations between the elapsed time since thestart of data transmission by the conventional setup on the one hand andtransmission rates on the other hand. The transmission rate at the startof transmission is zero. When an acknowledgement is received upon elapseof the time period RTT, the transmission rate is raised by apredetermined level for the next transmission. This transmission ratecontrol is repeated in response to the feedback informationcorresponding to the transmitted packets in a manner similar to how theinventive transmitting apparatus 11 carries out its communication. As aresult, the stable transmission rate B_(stable) is reached a time periodT0 after the start of data transmission, which is later than the timeT1.

As described above, the transmitting apparatus 11 reduces the timerequired to reach the stable transmission rate B_(stable) by a timeperiod (T0-T1) compared with the conventional setup. In the example ofFIG. 9, the transmission rate is shown raised by the same predeterminedlevel every time feedback information is received. In practice, however,the amount of the rise in the transmission rate is varied every time thetransmitting apparatus 11, given the feedback information from thereceiving apparatus 13, causes the rate control unit 25 to determine thetransmission rate for the next data transmission to the receivingapparatus 13 (the same applies to the conventional setup as well).

Also with regard to the example of FIG. 9, the time period RTT (aplateau period in which the transmission rate remains unchanged on thestaggered lines L1 and L2) following each transmission of video datauntil the receipt of an acknowledgement (feedback information) wasindicated as constant. In practice, however, each time period RTT variesillustratively depending on the traffic status of the network 12. Thelonger the time period RTT, the greater the difference between thescheme of this invention and the conventional setup in terms of how longit takes to reach the stable transmission rate B_(stable) (i.e., time(T0-T1)). In other words, the inventive scheme is more effective ataverting the slow-start problem. A typical situation in which the timeperiod RTT is prolonged is where data transmissions are carried out viasatellite.

Obviously, the higher the initial transmission rate B₁ (FIG. 9)determined by the initial rate determination unit 24, the more effectivethe transmitting apparatus 11 is in circumventing the slow-start problemas opposed to the conventional setup.

According to this invention, as described above, the transmission ratethat satisfies the minimum acceptable picture quality is determined asthe initial transmission rate. When the transmission of data is startedat the initial transmission rate thus determined, it is possible tobypass the slow-start problem that has plagued data transmissions.

According to the invention, there is no need for the sender side to sendto the receiver side a packet for measuring the bandwidth on the networkand to wait for an outcome of the transmission (i.e., feedbackinformation) from the receiver side. That means data can be transmittedwithout delay.

FIG. 10 is a block diagram showing a typical structure of thetransmitting apparatus 11 practiced as the second embodiment of theinvention. Of the reference numerals in FIG. 10, those already used inFIG. 2 designate like or corresponding parts, and descriptions of theseparts will be omitted where redundant. More specifically, thetransmitting apparatus 11 in FIG. 10 has basically the same structure asthat of its counterpart in FIG. 2 except that the initial ratedetermination unit 24 is replaced by another initial rate determinationunit 61.

As in the case of the initial rate determination unit 24 in FIG. 2, theinitial rate determination unit 61 in FIG. 10 is supplied with theproperty of pictures that are acquired by the picture acquisition unit21 or sent from outside the apparatus 11. Like the initial ratedetermination unit 24 in FIG. 2, the initial rate determination unit 61is fed with information indicating the encoding method designated by theuser manipulating the operation unit 27, the information coming from theoperation unit 27. Like the initial rate determination unit 24 of FIG.2, the initial rate determination unit 61 determines the minimumacceptable picture quality based on the picture property and encodingmethod in effect, decides on the transmission rate that satisfies theminimum acceptable picture quality thus determined, and supplies therate to the rate control unit 25 as the initial transmission rate.

FIG. 11 shows a typical internal structure of the initial ratedetermination unit 61 in FIG. 10. Of the reference numerals in FIG. 11,those already used in FIG. 3 designate like or corresponding parts, anddescriptions of these parts will be omitted where redundant. Morespecifically, the initial rate transmission unit 61 in FIG. 11 hasbasically the same structure as that of its counterpart in FIG. 3 inwhich the external interface unit 41, acceptable picture qualitydetermination unit 42, and transmission rate determination unit 44 arethe same as those in FIG. 3.

What makes the initial rate determination unit 61 in FIG. 10 of thesecond embodiment different from its counterpart in FIG. 3 is theabsence of the database 43 as part of the first embodiment. With thefirst embodiment, the table associating application properties withminimum acceptable picture qualities and the data representing relationsbetween picture motions and the minimum acceptable picture qualities,shown in FIGS. 4A and 4B, are supplied from the database 43 to theacceptable picture quality determination unit 42. With the secondembodiment, by contrast, the table and the data are supplied to theacceptable picture quality determination unit 42 from outside thetransmitting apparatus 11 via the external interface unit 41.

That is, the external interface unit 71 is supplied, from outside thetransmitting apparatus 11, with the same table associating applicationproperties with minimum acceptable picture qualities and the same datarepresenting relations between picture motions and the minimumacceptable picture qualities as those retrieved from the database 43shown in FIG. 3. From the external interface unit 71, the table and thedata are forwarded to the acceptable picture quality determination unit42.

Illustratively, the external interface unit 41 may be a networkinterface similar to the network interface unit 26 of FIG. 9. It isassumed that the external interface unit 41 is connected to a server(not shown) on a network such as the Internet. The server is assumed toretain the table associating application properties with minimumacceptable picture qualities as well as the data representing relationsbetween picture motions and the minimum acceptable picture qualities,with the stored table and data updated as needed. The external interfaceunit 41 retrieves such table and relational data from a source externalto the transmitting apparatus 11 and forwards what is retrieved to theacceptable picture quality determination unit 42.

In the same manner as with the first embodiment of FIG. 3, theacceptable picture quality determination unit 42 determines the minimumacceptable picture quality and supplies it to the transmission ratedetermination unit 44. That is, based on the table associatingapplication properties with minimum acceptable picture qualitiessupplied from the external interface unit 41, the acceptable picturequality determination unit 42 determines the minimum acceptable picturequality D_(i) (i=one of 1 through 4) corresponding to the applicationproperty sent from the operation unit 27. If the picture motion iscalculated at ml from the video data supplied by the picture acquisitionunit 21, the acceptable picture quality determination unit 42 determinesthe minimum acceptable picture quality D_(m1) based on the picturemotion m1 through the use of the relationship D=f_(x)(m) which comesfrom the external interface unit 41 and is shown in FIG. 4B. Then theacceptable picture quality determination unit 42 decides on thedefinitive minimum acceptable picture quality D and supplies it to thetransmission rate determination unit 44.

In the same manner as with the first embodiment in FIG. 3, thetransmission rate determination unit 44 determines the transmission ratethat satisfies the minimum acceptable picture quality sent from theacceptable picture quality determination unit 42, and supplies the rateto the rate control unit 25 (FIG. 9) as the initial transmission rate.

With the above-described second embodiment of this invention, the tableassociating application properties with minimum acceptable picturequalities and the data denoting relations between picture motions andthe minimum acceptable picture qualities were shown supplied fromoutside the transmitting apparatus 11 through the external interfaceunit 71 as the basis on which the acceptable picture qualitydetermination unit 42 determines the minimum acceptable picture quality.Alternatively, the user (i.e., the person who has video data transmittedor received) may explicitly set the minimum acceptable picture qualitythat may be sent to the acceptable picture quality determination unit 42via the external interface unit 71. As another alternative, the user mayexplicitly establish the minimum acceptable picture quality bymanipulating the operation unit 27. In turn, the operation unit 27supplies the established quality to the acceptable picture qualitydetermination unit 42. If the user explicitly sets the minimumacceptable picture quality, the acceptable picture quality determinationunit 42 forwards the supplied picture quality unchanged to thetransmission rate determination unit 44.

Where the second embodiment is in use, any updates made from numerousexperiments and experience to the table associating applicationproperties with minimum allowable picture qualities and to the datadenoting relations between picture motions and the minimum allowablepicture qualities may be supplied without delay to the acceptablepicture quality determination unit 42 via the external interface unit71. In terms of up-to-dateness, the second embodiment is thus preferredto the first embodiment in which the database 43 is set up inside thetransmitting apparatus 11.

The second embodiment of the above-described structure provides the sameeffects (shown in FIG. 9) as those offered by the first embodiment. Thatis, where streaming data is to be transmitted, the transmission ratethat satisfies the minimum acceptable picture quality is determined asthe initial transmission rate so that transmission of the data isstarted at that initial rate. This arrangement provides datatransmission in such a manner as to avert the slow-start problem. It isalso possible to transmit data without delay because there is no needfor the sender side to send to the receiver side a packet for measuringthe bandwidth on the network and to wait for the result of thetransmission (feedback information) from the receiver side.

In the above-described embodiments of the invention, the transmittingapparatus 11 was shown transmitting video data. However, this is notlimitative of the invention. Alternatively, this invention applies tosetups whereby diverse kinds of streaming data including movingpictures, still pictures, sounds, presentation data, and video games aretransmitted. It is also possible for the transmitting apparatus 11 tosend data other than streaming data.

In the embodiments described above, the application property and theimaging device property were shown supplied by the user manipulating theoperation unit 27 or sent from outside the transmitting apparatus 11through the external interface unit 41. Alternatively, the transmittingapparatus. 11 may be arranged to determine by itself these propertiesbased on the pictures acquired by the picture acquisition unit 21.

In the above embodiments, the picture size was shown determined by thetransmission rate determination unit 44 based on the video data suppliedfrom the picture acquisition unit 21. Alternatively, the picture sizemay be designated by the user manipulating the operation unit 27. Inturn, the operation unit 27 feeds the designated picture size to theinitial rate determination unit 61.

In the embodiments above, the picture encoding method was showndesignated by the user manipulating the operation unit 27.Alternatively, an appropriate encoding method may be establishedbeforehand as the default. Only when the user designates a differentencoding method, the designated method may be replaced therewith.

The series of steps and processes described above may be executed eitherby hardware or by software. In any case, the transmitting apparatus 11may be constituted illustratively by a personal computer such as oneshown in FIG. 12.

In FIG. 12, a CPU (Central Processing Unit) 301 performs diverseprocesses in keeping with the programs stored in a ROM (Read OnlyMemory) 302 or with those loaded into a RAM (Random Access Memory) 303from a storage unit 308. The RAM 303 also accommodates data that may beneeded by the CPU 301 in carrying out its processing.

The CPU 301, ROM 302, and RAM 303 are interconnected via a bus 304. Aninput/output interface 305 is also connected to the bus 304.

The input/output interface 305 is connected with diverse components.They include an input unit 306 formed illustratively by a keyboard andmouse, an output unit 307 constituted by a display device such as a CRT(Cathode Ray Tube) or an LCD (Liquid Crystal Display) as well as byspeakers, the storage unit 308 composed of a hard disk drive or thelike, a communication unit 309 having a modem and a terminal adapter,and an imaging unit 331 made up of image devices such as CCD (ChargeCoupled Devices) or CMOS (Complementary Metal Oxide Semiconductors). Thecommunication unit 309 performs communications over the network such asthe Internet. The imaging unit 311 takes pictures of an object andsupplies the CPU 301 and related components with video datarepresentative of the imaged object by way of the input/output interface305. The CPU 301 controls illustratively the processes performed by theacceptable picture quality determination unit 42 and transmission ratedetermination unit 44 in the initial rate determination unit 24 as wellas by the picture encoding unit 22, transmission unit 23, and ratecontrol unit 25. The communication unit 309 controls the processescarried out by the network interface unit 26 and by the externalinterface unit 41 in the initial rate determination unit 24, amongothers.

The input/output interface 305 is further connected with a drive 310 asneeded. A recording medium such as a magnetic disk 321, an optical disk322, a magneto-optical disk 323, or a semiconductor memory 324 is loadedinto the drive 310. Computer programs may be retrieved from the loadedrecording medium and installed as needed into the storage unit 308.

In this description, the steps which are stored on the recording mediumand which describe the programs to be executed represent not only theprocesses that are to be carried out in the depicted sequence (i.e., ona time series basis) but also processes that may be performed parallellyor individually.

INDUSTRIAL APPLICABILITY

According to the above-described transmission controlling apparatus,transmission controlling method, recording medium, and program of thisinvention, it is possible to start transmitting data over the networkinstantaneously while circumventing the slow-start problem using theinventive arrangements.

1. A transmission controlling apparatus for controlling transmission ofdata, the apparatus comprising: quality determining means fordetermining quality of said data in keeping with a property of saiddata; transmission rate determining means for determining a transmissionrate in accordance with the quality determined by said qualitydetermining means; and transmission rate controlling means forcontrolling the transmission rate of said data so that said data willstart to be transmitted at the transmission rate determined by saidtransmission rate determining means.
 2. The transmission controllingapparatus according to claim 1, wherein said data constitutes pictures,and the property of said data is a picture property.
 3. The transmissioncontrolling apparatus according to claim 2, wherein said pictureproperty is at least one of an application property, a content property,and an imaging device property.
 4. The transmission controllingapparatus according to claim 2, further comprising storing means forstoring the data of which the quality is associated with said pictureproperty; wherein said quality determining means determines said qualitybased on the data stored in said storing means.
 5. The transmissioncontrolling apparatus according to claim 1, wherein said dataconstitutes pictures encoded by a predetermined encoding method; andwherein said transmission rate determining means determines saidtransmission rate based on a picture size of said pictures and on arelationship between the quality associated with said encoding method onthe one hand and said transmission rate on the other hand.
 6. Thetransmission controlling apparatus according to claim 1, furthercomprising information inputting means for inputting information aboutthe property of said data from outside of said transmission controllingapparatus; wherein said quality determining means determines saidquality in accordance with said information input by said informationinputting means.
 7. The transmission controlling apparatus according toclaim 1, wherein said transmission rate controlling means controls thetransmission rate of said data so that after the transmission of saiddata has started, the rate of said transmission will not be loweredbelow said transmission rate supplied from said transmission ratedetermining means.
 8. The transmission controlling apparatus accordingto claim 1, wherein said transmission rate controlling means controlsthe transmission-rate of said data so that in case of a communicationtime-out of said data, the transmission of said data will be resumed atthe transmission rate determined by said transmission rate determiningmeans.
 9. A transmission controlling method for controlling transmissionof data, the method comprising the steps of: determining quality of saiddata in keeping with a property of said data; determining a transmissionrate in accordance with the quality determined in said qualitydetermining step; and controlling the transmission rate of said data sothat said data will start to be transmitted at the transmission ratedetermined in said transmission rate determining step.
 10. A recordingmedium which stores in computer-readable fashion a program forcontrolling transmission of data, said program comprising the steps of:determining quality of said data in keeping with a property of saiddata; determining a transmission rate in accordance with the qualitydetermined in said quality determining step; and controlling thetransmission rate of said data so that said data will start to betransmitted at the transmission rate determined in said transmissionrate determining step.
 11. A program for controlling transmission ofdata and for causing a computer to execute a procedure comprising thesteps of: determining quality of said data in keeping with a property ofsaid data; determining a transmission rate in accordance with thequality determined in said quality determining step; and controlling thetransmission rate of said data so that said data will start to betransmitted at the transmission rate determined in said transmissionrate determining step.